Mata to United makes no sense whatsoever bar appeasement of the fans there.
He plays best in the Hole, they have Rooney and kagawa there.
He's not been too great this season playing on the wing, that's the only position they'll have space for him.
He'll encounter the exact same problem there as he has here, if he plays every game with Rooney and he plays on the wing, he'll be in poor form. Going to United makes no sense. PSG is an option, but will they change their 4-3-3 system to accommodate mata, I don't think so yet. Lavezzi and Lucas fit the system more than Mata, so he'll also be on the bench. Cavani and Ibra are beasting it this season, so he's not taking their spots in a million years.
Dortmund don't have the money, Bayern he'll be on the bench, Barca he'll be on the bench(nor would he go there) Madrid sold Ozil, why would they buy Mata, Arsenal don't need him, Liverpool won't get him unless they make CL this summer Spurs won't get him. I'm pretty confident about the situation.